1. Field of the Invention
The present invention relates to a method of fabricating a T-type gate and, more particularly, to a method of fabricating a T-type gate capable of facilitating a compound semiconductor device manufacturing process, enhancing the yield, and reducing the manufacturing cost by forming two kinds of patterns from one kind of photoresist layer using electron beam and photolithography technologies and by interposing a blocking layer between upper and lower photoresist layers for reversing the patterns.
2. Discussion of Related Art
In general, in methods of fabricating a compound semiconductor device such as a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), a heterojunction bipolar transistor (HBT) and so on, which have ultra-high frequency characteristics as a high performance transistor, small parasitic elements of a gate electrode, high reliability, and high operating speed, a process of fabricating a T-type gate, which is a core process, individually adapts photoresist layers depending on each pattern in order to form a body and a head of the T-type gate. The process has difficulties in implementing the devices since it is difficult to realize a fine pattern, the process becomes complicated, and the device cannot be easily manufactured.
In a conventional method of forming a T-type gate, a fine body pattern of the T-type gate is formed by exposing and developing a first photoresist using electron beams. However, in forming the fine pattern using the electron beams, it is more difficult to adapt the photoresist layer on an insulating layers rather than a metal layer due to an electron charging effect.
In addition, in a process of transferring the fine pattern to a lower insulating layer using a predetermined photoresist layer as a mask, a two-step etching process including a dry etching process for allowing a portion of the insulating layer to remain in order to prevent the substrate from being damaged and a wet etching process for removing the remaining layer without damaging the substrate is required, thereby lengthening the process.
As described above, according to the conventional method, many steps are required and it is difficult to form the fine pattern. Also, a metal lift-off process cannot be smoothly performed since the metal is not deposited with a low step coverage required.